Micro-wave test set an/spg{14 51b radar

ABSTRACT

A microwave test set for checking the operation of a waveguide and its components while the waveguide is still mounted on equipment. A signal of known power level from a variable signal source is injected at the front end of the antenna system and by the use of an assembly of three C band hybrid T assemblies power of equal amplitude, and in the proper phase, is simultaneously inserted in each quadrant of a four quadrant cluster. This input power is then compared with power measured at the end of the waveguide run to determine the amount of attenuation present.

United States Patent 1191 Belli Nov. 13, 1973 MICRO-WAVE TEST SETAN/SPG-51B Primary Examiner-T. H. Tubbesing RADAR Attrney-Edgar J.Brower, Thomas 0. Watson, Jr. 76 Inventor: William F. Belli, 3503Shelton Rd., and Rbert Anders Portsmouth, Va. 23703 22 Filed: Jan. 27,1970 [57] ABSTRACT [21] Appl. No.: 10,107 A microwave test set forchecking the operation of a waveguide and its components while thewaveguide is still mounted on equipment. A signal of known power [52]US. Cl. 343/17.7, 343/703 level f a variable Signal Source is injectedat the [51] hit. Cl. G018 7/40 front end of the antenna system and bythe use of an [58] Field Of Search 343/17.7, 703 assembly of three C bad hybrid T assemblies power 0 of equal amplitude, and in the properphase, is simul- [56] References taneously inserted in each quadrant ofa four quadrant UNITED STATES PATENTS cluster. This input power is thencompared with power 3,153,760 10/1964 Henderson 343 177 x measured atthe end of the a gu r n t d t 3,225,295 12/1965 Altman et al. 343/1717 Xmine the amount of attenuation present. 3,357,017 12/1967 Jewell 343/17]3,363,249 1/1968 Hershey et al. 343 177 6 Claims, 7 Drawing Figures EmmiFEED C-BAND memo T's 72/ SYSTEM i I Z0 32 pl 55 E POWER 3&- 22 BRIDGE 505-0 I 34 Lo 20 i i 1 COMPLEX 11 2 U ON-MOUNT 4 WAVEGUIDE P /5 1 RUN l6i1 LI 221 i SIAGFAAQL IISNPUT 54 PS EOBIER SOURCE el n i etE 8N% rs|ot|ATTENUATOR CIRCUITS 62 DATA :051:11: gq 34 0e 66 JIQ-NORMAL INSERTIONPOINT FOR MOS PATENTEBMBMEIHH 3.772.700 SHEET HP 4 INVENTOR F/fi. IWILL/AM F BELL! AGENT PATENTEDHHVIBIHB 3772700 SHEET 3 BF 4 MICRQzWAYETESJI. .SWET AN/SBG:51B RADAR.

STATEMENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates to testequipment and more particularly to test equipment in the form of amicrowave test set which is used to check the operation of a waveguidefor the AN/SPG-S 1B radar.

It has been the experience in the past of electronic repair personnelthat the lack of proper testing devices makes it very difficult andcostly to properly evaluate the operating condition of the complex onmount waveguide run of the ANISPG-51B radar. The only method that hasbeen available to the engineer in the past is to physically disassembleand visually inspect the wavemately 1 week. Furthermore, this prior artsystem requires collimation of the antenna systems after reassembly andthe possibility of destroying null fill characteristics if improperhandling of components occurs. There have been several instances in thepast where salt water has been introduced into the complex waveguidesystem due to the rupture of one of the numerous components in thiswaveguide run. The engineer on the job very correctly has the obvioussection replaced, but has no means to determine if a appreciabledegrading of other parts of the waveguide run has occurred due to thisintroduction of salt water into the system, unless he has the ship puton a repair status and has all of the hardware disassembled forinspection. Obviously, an operational ship must have justification forthis action. As the situation is at the present, the engineer might justas well flip a coin to make this recommendation, due to lack of dataand/or the means to obtain it.

SUMMARY OF THE INVENTION IN view of the above listed disadvantages andshort comings of the prior systems the test set of the present inventionhas been constructed to evaluate the condition of this waveguide run interms of electrical loss. The system provides a tester which is easy touse, one which is readily applied to a radar without having to dismantlethe radar system, and one which provides extreme accuracy in itsreadings. Through the use of this tester deterioration and weak spots inthe waveguide run can easily be detected even though in most cases thisdeterioration is not obvious to the engineer making the test and isdiscovered only through the process of taking accurate electricalmeasurements.

OBJECTS OF THE INVENTION test set to establish and record the actualelectrical loss 65 in complex waveguide systems.

Another object of the present invention is the provision of a means toisolate a section of waveguide or a microwave component that iscontributing excessive loss in the waveguide system.

Still another object is the provision of a waveguide test set which maybe used without having to dismantle the equipment.

Still another object is the provision of a waveguide test set which doesnot require collimation of the antenna and avoids improper handling ofcomponent parts.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a diagram of the mannerin which the hybrid junctions are connected;

FIG. 2 shows a plan view of the tester;

FIG. 3 shows a side elevation of the tester;

FIG. 4 shows an end elevation of the tester;

FIG. 5 shows another end elevation of the tester; and

FIG. 6 shows an overall schematic of the tester.

FIG. 7 shows an alternate embodiment of the attenuator 56 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of thedrawings there is shown a diagram of the manner in which the three Cband hybrid T assemblies are connected. It will be noted that each ofthe assemblies has four arms or terminals, such as a shunt arm, a seriesarm, and two phase shifted arms. Looking at FIG. 1 it will be seen thatan electromagnetic signal is applied to shunt arm 16 of the centerhybrid junction 10. The series arm 20 of this junction is connected to adummy load 18 which has a value equal to the characteristic impedance ofthe arm. The two phase shift arms 24 and 22 produce signals which havebeen phase shifted and have an electrical value of one-half of the inputsignal. The output of arm 22 is then connected to shunt arm 26 of hybridjunction 12, this junction producing outputs on arms 30 and 28,respectively, which have again been cut in half so that its output isone-fourth of the applied electrical potential. The series arm ofjunction 12 is also connected to a dummy load 34 which is equal in valueto the characteristic impedance of the arm.

The other output signal from the hybrid junction 10 as appearing on arm24 is applied; as an input to shunt arm 36 of hybrid junction 14, theseries arm of this junction 42 being connected to a dummy load 44 alsoequal to the characteristic impedance of the arm. Hybrid junction 14also produces two outputs on its arms 38 and 40, respectively, whichlike the output from hybrid junction 12 is also equal to one-fourth ofthe input potential.

FIGS. 2, 3, 4 and 5 show various elevation views of the hybrid junctionassembly, with corresponding parts having the same identifying numeralin the various figures. From FIGS. 1 5 inclusive it can now be seen thatthe hybrid junction assembly produces four outputs of like amount asfrom arms 28, 30, 38, and 40, and these outputs are applied to fourwaveguides, 46, 48, 50 and 52. These waveguides of course, are thosebelonging to the four quadrant cluster of the antenna feeding system ofthe radar under test.

In FIG. 6 there is shown a complete test equipment set up including theC band hybrid T arrangement previously described and shown in thisfigure within the dotted lines. Input terminal 54 is used to apply thesignal input which is obtained from the STAMO of the radar under test.Connected to the input terminal 54 there is a 150 db variable attenuator56 for adjusting the power of the input signal before it is applied tohybrid junction 16. Also connected to the input of hybrid T junction 16there is a power bridge 58, the function which will be described morefully hereinafter. The structure of the hybrid T assembly and componentparts are the same as those described for FIG. 1, the output of thisassembly being connected to an antenna feed system shown generally as72. The antenna feed system 72 consists of four similar waveguidesections 48, 50, 52, and 46 their outputs all being connected inparallel and connected to an on mount waveguide run 60. The output ofwaveguide run 60 in turn passes through a test point 62 before thesignal is applied to the receiver circuits 64, the signal then beingpassed on to a data convertor receiver 66 where the output is dividedbetween a data convertor circuit 70 and a true RMS meter 68.

In FIG. 7 there is shown an alternative embodiment of the attenuator 56of FIG. 6. Instead of the 150 db variable attenuator shown in FIG. 6,three 50 db variable attenuators 82, 84 and 86 connected in series maybe used.

Turning now to the structure and theory of operation of the invention itwill be recalled that the intregrated hybrid T assembly consists ofthree each hybrid Ts, l0, l2 and 14, three each dummy loads 18, 34, and44 to terminate series arms 20, 32, and 42 into their characteristicimpedance and two each N type feed through connectors. The antenna feedsystem 72 (FIG. 6) is a modified feed horn having its window portion cutfrom the assembly. A shorting plate was installed across the foursections of open waveguide 48, 60, 52 and 46 and each section of thewaveguide was machined to accommodate the dipole and N type connectorfrom a waveguide to coaxial adaptor. The intregrated hybrid T assemblywas then mounted and electrically connected to the modified feed horn.

Preparation for test requires removal of the normal feed horn assembly,and replacement with the modified feed horn of the test set. The radarreceiver should be checked to insure proper crystal currents and properAGC set at data convertor receiver 66. Zero knot clutter is selected andbreak track is depressed and maintained depressed throughout the entiretest. A true RMS meter 68, or equivalent, is connected to the dataconvertor receiver 66 output. The remaining test equipment should beconnected as shown in FIG. 6.

Procedure for making the test is as follows:

Step I: The waveguide switch is temporarily closed at this time toeliminate possibilities of destroying mixer crystals by the applicationof too high a power level.

Step 2: The variable attenuators 56 are now adjusted to yield a zero dbreading on power bridge 58. The sum of the three attenuator settings arenow recorded as reading A, test I on a work sheet. After reading A isobtained the attenuators should be set to 50 db each and waveguideswitch opened.

Step 3: While observing the true RMS meter 68 adjust the variableattenuators 56 until the output of data convertor receiver 66 yields mvon the true RMS meter. The sum of the. three'attenuators is now recordedasreading B, test l on the work sheet. (This step should be repeatedfour times, each time using different combinations of attenuatorsettings and the average reading taken.) The relative MDS for test 1 isnow computed as reading B reading A l and recorded on theworksheet. The+1 db is to account for insertion loss of the modified feed horn 72.Reference level of 100 mv was selected to insure that the linear portionof the radar receiver gain curve is being used. I I

Step 4: The output of the variable attenuators and the power bridge isnow connected to the 34 db test point 62.

Step 5: The variable attenuators are now adjusted until the power bridgeindicates 0 db. The sum of the three attenuator settings is now recordedas reading A, test 2 on a worksheet.

Step 6: Again the variable attenuators are adjusted to yield a 100 mvoutput of data convertor receiver 66 as read on true RMS meter 68. Thesum of the three attenuators settings is recorded as reading B, test 2on the worksheet. (This test should be repeated 4 times, each time usingdifferent combinations of the attenuator settings and the averagereading taken.) The relative MDS for test 2 is now computed as reading Breading A 34. The +34 is compensation for 34 db insertion loss at point62.

Step 7: A complex waveguide loss is now computed as relative MDS lrelative MDS 2 and recorded on the worksheet.

From the above description of the structure and operation of theinvention it can be seen that the disclosed microwave test set providesan accurate, inexpensive, and rapid means of evaluating a complexwaveguide system in terms of electrical loss and that the data obtainedby the test set can be very useful in the early detection of waveguidedeterioration so that remedial action can be promptly taken.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings.

What is claimed is:

l. A microwave test set for evaluating an on mount waveguide run of aradar comprising:

means for receiving a test signal from the radar;

attenuating means for adjusting the strength of the test signal;

power measuring means for measuring the strength of the test signalbefore it is applied to the waveguide run;

means for applying the test signal to the waveguide run;

receiver means connected at the end of the waveguide run;

a data convertor receiver connected to the receiver means; and

a true RMS meter connected to the data convertor receiver.

2. The microwave test set of claim 1 wherein the test signal is producedby the STAMO of the radar.

3. The microwave test set of claim 1 wherein the attenuating meansconsists of three series connected 50 db attenuators.

4. The microwave test set of claim 3 wherein the means for applying thetest signal to the waveguide run consists of three C band hybrid Tassemblies.

5. The microwave test set of claim 4 wherein the means for applying thetest signal to the waveguide run 5 further consists of a feed hornconnected between the hybrid T assembly and the waveguide run.

four quadrant cluster of the radar antenna.

1. A microwave test set for evaluating an on mount waveguide run of aradar comprising: means for receiving a test signal from the radar;attenuating means for adjusting the strength of the test signal; powermeasuring means for measuring the strength of the test signal before itis applied to the waveguide run; means for applying the test signal tothe waveguide run; receiver means connected at the end of the waveguiderun; a data convertor receiver connected to the receiver means; and atrue RMS meter connected to the data convertor receiver.
 2. Themicrowave test set of claim 1 wherein the test signal is produced by theSTAMO of the radar.
 3. The microwave test set of claim 1 wherein theattenuating means consists of three series connected 50 db attenuators.4. The microwave test set of claim 3 wherein the means for applying thetest signal to the waveguide run consists of three C band hybrid Tassemblies.
 5. The microwave test set of claim 4 wherein the means forapplying the test signal to the waveguide run further consists of a feedhorn connected between the hybrid T assembly and the waveguide run. 6.The micowave test set of claim 1 wherein the means for applying the testsignal to the waveguide run includes means for produding fourequal-amplitude, in-phase signals and for injecting said signals intothe four quadrant cluster of the radar antenna.